This terrible trauma that happened to Anjali can affect Arnav and Khushi in two ways. One way is that Arnav turns to Khushi during this painful time and will use her as an anchor - he will seek comfort in her and their bond will strengthen. This way Arnav has fully given himself to Khushi and it will be up to Khushi to make sure he stays strong for Anjali's sake. They will both work together and rely on one another and slowly rebuilt Anjali.
Another way is that Arnav will only focus on Anjali and would retreat from Khushi - he will decline Khushi's support and strength but will instead push her away. He will in guilt blame himself that he was occupied with Khushi and lost focus of his sister who needed him. This way will weaken Arnav and Khushi's bond as Khushi would feel that Arnav blames her and leading her to blame herself. This will make them suffer separately and that will also make sure that Anjali can never heal.
I so pray that the Iss Pyaar team has decided to go with option number one - that will calm most of the fans and also help with the trp ratings. This track can also make sure that Iss Pyaar stays unique with it's concept.